It has been known that by employing specific low dispersion glass having a high Abbe number and a large deviation from a standard line of a relative partial dispersion (anomalous dispersion) in a combination with high dispersion glass having a large difference of refractive indexes depending on various wavelengths of light, it is possible to effectively correct secondary chromatic aberration (Patent Documents 1 and 2).
However, it is difficult to mold the specific low dispersion glass and also difficult to process the specific low dispersion glass into a complex form such as an aspherical shape. Further, impact resistance of lenses made of such specific low dispersion glass is low, and its handling property is poor.
On the other hand, as a resin material for lenses, ZEONEX (manufactured by ZEON CORPORATION), APEL (manufactured by Mitsui Chemicals, Inc.), etc. are known. However, since their Abbe number is low at a level of about 55 and their anomalous dispersion is also low, their properties required for chromatic aberration-free lenses are insufficient.
Patent Document 1: JP-A-7-199123 (Means for solving the problem)
Patent Document 2: JP-A-2004-333768 (paragraph [0040])